1. Field of the Invention
The present invention relates to a semiconductor light emitting element, a method for manufacturing the semiconductor light emitting element, and a light emitting device.
2. Related Art
In recent years, semiconductor light emitting elements are widely used for display devices, lighting systems, recording devices, and the likes. Particularly, semiconductor light emitting diodes (LEDs) that do not involve induced emission are used as display devices, because of its high luminance. Also, as one of the latest applications, LEDs are used as lights. For instance, as alternative lights for fluorescent lights, solid-state illumination has been developed and is being actively put into practical use by combining fluorescent lights with semiconductor light emitting elements of short wavelengths in the range of green and ultraviolet that include nitride-based semiconductors such as GaN. To actually replace the conventional solid-state illumination with the alternative lights, it is important to optimize the combination of a light emitting element such as a light emitting diode (LED) including a nitride-based semiconductor and a fluorescent material, and to obtain natural white light very similar to the sunlight.
There have been combinations of blue LEDs and yellow fluorescent materials to obtain general white light. However, a combination of a near-ultraviolet LED chip and a RGB fluorescent material can obtain the light most similar to the sunlight, and can also achieve more excellent color rendering properties than any combination of a blue LED and a yellow fluorescent material.
However, by such a related technique, it is necessary to apply a fluorescent material to a LED chip, and the color rendering properties are affected by the application method. Therefore, a complicated manufacturing process and fine adjustment are required. Also, there is the problem that it is difficult to obtain uniform reproducibility and to readily obtain a white light source.
Further, there is the problem that an increase in In (indium) composition ratio for controlling the wavelength of the LED chip combined with a fluorescent material leads to an increase of defects in non-light emitting portions due to uneven concentration and a decrease in crystal quality. Therefore, it has been difficult to obtain high-quality crystals with high In composition ratios.
Also, there is the problem that the light emission efficiency with respect to the power input of a semiconductor light emitting element used as a light is lower than the light emission efficiency of a fluorescent light.
Meanwhile, GaN-based semiconductor light emitting elements that can emit high-power ultraviolet rays even with a low In composition ratio have been developed (see JP-A 2003-258302 (KOKAI), for example). The light emitting element disclosed in JP-A 2003-258302 (KOKAI) has a stacked structure formed with GaN-based crystalline layers on a substrate having concave and convex portions on its surface, and the stacked structure includes an InGaN-based light emitting layer. The In composition in the light emitting layer is modulated in the plane in accordance with the concave and convex portions of the substrate. However, the light emission wavelength range of this light emitting element is not wide, and color rendering properties that are close to those of white light cannot be obtained.
As described above, the related combination of a light emitting element and a fluorescent material to obtain white light involves a complicated manufacturing process, and a highly controlled manufacturing technique is required to form a light emitting element having a high In composition ratio for wavelength control.
Also, there have been no semiconductor light emitting elements with excellent color rendering properties.